Hybrid microelectronic devices such as Lange couplers have been conventionally manufactured on a variety of substrate materials using various techniques such as thick film, low temperature co-fired ceramic (LTCC), and thin film technology. Hybrid devices are used in many microelectronics applications in the defense, medical, communications, computer, automotive, and infrared imaging industries, as well as in many other applications. In all of these industries there is continuous demand for devices that offer improved performance and function, especially at higher electrical frequencies. In order to satisfy these demands, the number of passive devices (capacitors, inductors, and resistors) designed into microelectronic devices continues to grow. For instance, a typical cellular phone product may contain 400 components, with less than 20 devices being active (i.e., semiconductors) and the 380 or more devices being passive devices.
Along with demands for better performance are also requirements to provide products that are less expensive and smaller in size. It is reported that the passive components in a cellular phone product can occupy 80% of the printed circuit board area and account for 70% of the product assembly costs. Thus, there is clear need to reduce the size and cost of the passive devices required in microelectronic devices.
Of the hybrid circuit fabrication techniques, thin film technology is extremely well suited for use in RF/microwave, wireless, and optical transmission technologies because of its ability to provide high quality features, extremely dense packaging, and a large range of integrated features.
The current state of the art in thin film hybrid microelectronic manufacturing offers cost effective, high reliability methods for integrating conductors, inductors, and resistors onto the same thin film hybrid circuit device but not capacitors and interconnects (i.e. connections between devices and multiple layers).
Presently, capacitors are typically purchased individually and attached to the thin film devices using various surface mount die attach techniques. The individual chip capacitors take up valuable space, require much assembly labor, and can decrease reliability due to assembly problems.
Interconnects are often required to interconnect components and devices and to attach to the center of spiral inductors and power splitters such as Lange couplers. Current technology uses wire or ribbon bonding or air bridge type techniques to make individual interconnects. Wire or ribbon bonds can add higher costs and sometimes cause high frequency performance problems due to bond inconsistencies, different bond shapes or the bonds falling over and shorting to conductor lines that they are crossing over. Air bridges are expensive and difficult to produce because of their inherent complexity.
Thus, there is a clear need for a reliable fabrication method that offers both Lange couplers, capacitors, and integrated interconnects. It is especially desirable that this method provides features that are usable from DC to very high operating frequencies. The prior art does not satisfy this need.
A recent approach to the integration of capacitors and interconnects has concentrated on fabricating these devices on silicon wafers. See MARC DE SAMBER, NICK PULSFORD, MARC VAN DELDEN, ROBERT MILSOM; “Low-Complexity MCM-D Technology with Integrated Passives for High Frequency Applications”, The International Journal of Microcircuits and Electronic Packaging, Volume 21, Number 2, Second Quarter 1998, pgs 224-229 (ISSN 1063-1674) (International Microelectronics and Packaging Society).
This paper presented simple concepts for fabricating integrated capacitors, inductors, resistors, and interconnects on silicon wafers. However, processing thin film hybrid substrates offers unique challenges when compared to silicon wafers, and the teachings presented in this prior art are not directly applicable to thin film hybrid substrate processing. Additionally, the integration of reliable Lange coupler structures that can be easily manufactured within this context has not been addressed by the prior art.